Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$17.62	10.243%	$19.4248	$19.42	$19.40	$19.40
Purchase #2	$72.44	13.774%	$82.4179	$82.42	$82.40	$82.40
Purchase #3	$215.33	12.166%	$241.527	$241.53	$241.55	$241.50
Purchase #4	$115.71	10.163%	$127.4696	$127.47	$127.45	$127.50
Purchase #5	$113.33	9.474%	$124.0669	$124.07	$124.05	$124.10
Purchase #6	$50.61	6.133%	$53.7139	$53.71	$53.70	$53.70
Purchase #7	$140.37	5.627%	$148.2686	$148.27	$148.25	$148.30
7 purchase totals =	$725.41		$796.8887	$796.89	$796.80	$796.90